1. Field of the Invention
The invention relates to devices and methods of testing optical lines which consist of optic fiber cables and connectors interconnecting them.
2. Prior Art
FIG. 12 is a block diagram showing a configuration of a conventional optical line testing device. Herein, `A` designates an optical line (or a light transmission path) which is an object to be measured (or tested) by the device. In addition, there are provided a light pulse tester 1, optic fiber cables 2a to 2d, connectors 3a to 3c and a cable terminal set 4, wherein the optic fiber cables are interconnected together by the connectors. The light pulse tester 1 generates light pulses which are radiated to the optical line A. The light pulses propagate through the optic fiber cables 2a to 2d and the connectors 3a to 3c; then, the light pulses are reflected by the cable terminal set 4. So, the light pulses reflected propagate backward through the optical fiber cables 2a to 2d and the connectors 3a to 3c, so that they are returned to the light pulse tester 1. Thus, intensity of light is detected with respect to reflected light (or response light; i.e., reflected light pulse).
FIG. 13 shows an example of a response waveform, representing the response light, which is visually displayed on a screen of a display unit (not shown). Herein, each of waveform portions 5a to 5d indicates backward scattered light which exists within a space of an optic fiber cable. Based on a gradient of each waveform portion, it is possible to calculate a loss for each of the optic fiber cables 2a to 2d. Each of waveform portions 6a to 6c indicates Fresnel's reflection which occurs at each of the connectors 3a to 3c; and a waveform portion 7 represents Fresnel's reflected light at the cable terminal set 4. As described above, the light pulses, which are radiated from the light pulse tester 1, are subjected to scattering and reflection at some points of the optical line A; therefore, the display unit visually displays the response waveform of the response light which corresponds to sum of scattered light and reflected light.
In the conventional optical line testing device, a variety of switches and keys, which are provided on a panel face of an operation panel (not shown), are manipulated by a human operator to perform measurement on the waveform portions 5a to 5d, 6a to 6c and 7, in the response waveform of the response light, with respect to some items which are determined in advance. Thus, it is possible to measure lengths of the optic fiber cables 2a to 2d as well as positions and connection losses of the connectors 3a to 3c. In such measurement operations, simple manipulation of the keys should be frequently repeated. For example, in order to perform measurement on the aforementioned optical line with respect to connection loss, the conventional optical line testing device is controlled as follows:
At first, an LD key is manipulated to activate the light pulse tester 1, so that light pulses are radiated to the optical line A. Then, an AVERAGE key is manipulated to average an amount of response light which is received by the light pulse tester 1 in a certain period of time. After finishing the averaging, the LD key is manipulated again to stop operation of the light pulse tester 1.
FIG. 14 is an enlarged view showing a selected part of the response waveform shown in FIG. 13. Now, a SHIFT key is used to set a position of a measuring point on the response waveform, so that a visually displayed part of the response waveform is shifted in a desired direction. A rotary nob is manipulated to move a cursor 9 and locate it at a marker 8a, representing the measuring point, on the response waveform. Then, a MARKER key is used to select one of other markers 8b to 8d. If the marker 8b is selected, the display unit visually displays the level of the measuring point, which is designated by the marker 8a, as well as the level of a point designated by the marker 8b on the screen. So, level-entry work is carried out by reading values of those levels. A series of measuring operations, described above, are repeatedly carried out by manipulation of the MARKER key and rotary nob with respect to each Fresnel's reflection. After completion of the measuring operations, a SAVE key is manipulated so that all results of measurement are stored in a certain memory.
In the conventional optical line testing device, every time measurement is carried out with respect to one light transmission path, it is necessary to make settings for the cursor and markers by manipulating the aforementioned keys with respect to a specific point of Fresnel's reflection; and it is necessary to read a position of Fresnel's reflection and a connection loss as well. So, the conventional device should repeat the same operations with respect to other points of Fresnel's reflection. In other words, the conventional device suffers from a problem that measurement cannot be made simultaneously for multiple measuring points. In addition, there is another problem that as compared to time required for measurement in level of the measuring point, such time should be required for the settings of the cursor and markers.
Instead of the aforementioned optical line testing device, another device, having an event function, which is capable of carrying out measurement on multiple measuring points simultaneously. This type of device is designed such that a return loss, which is lower than a predetermined level, is automatically detected from the response waveform; and then, results of the measurement are displayed in the form of a list with respect to points on which the above automatic detection is performed. In other words, this type of device is designed to automatically perform detection of Fresnel's reflection whose return loss is lower than the predetermined level. This indicates that a measuring point is moved in response to a response waveform. In other words, it is not always possible for a human operator to perform measurement on a desired measuring point. In short, there is a problem that measurement is performed with respect to a measuring point which is not desired by the human operator. In addition, there is another problem in that precision of measurement is lowered in the case of a curved response waveform or in the case of a response waveform whose noise level is relative large. Moreover, there is a need to develop an advanced measuring function which is capable of automatically performing measurement on multiple measuring points without repeating a same work using manual operations described above.